These estimates come from a terrific analysis of the influence of mass media on U.S. government response to 5,000 natural disasters around the world from 1968 to 2002.
It shows pretty clearly that the amount of disaster relief provided by the U.S. varies with the level of television news coverage, and news outlets routinely fail to cover certain types of disasters (drought, famine, cold wave) and those that occur outside the U.S. or Europe. In the words of the authors:
The conclusion is that media induces extra relief to volcano and earthquake victims, at the expense of victims of epidemics, droughts, cold waves and food shortages…Network news also induces a relief bias against Africa, Asia and the Pacific. While the TV networks cover more than 15 percent of the disasters in Europe and South and Central America, they cover less than 5 percent of the disasters in Africa and the Pacific…The estimates suggest that it requires 45 times as many killed in an African disaster to achieve the same probability of media coverage as for a disaster in Europe. We conclude that media coverage induces extra U.S. relief to victims in Europe and on the American continent, at the expense of victims elsewhere.
News Droughts, News Floods, and U. S. Disaster Relief [pdf] by Thomas Eisensee & David Strömberg (2007)